I saw Jonathan in Blow Dry do a diagonal cut from fringe to back, but he didn't do a diagonal cut... he cut little 1/2 inch parallel steps from the fringe all the way down; not vertical notches but parallel like a stair step. Is this something I mistakenly saw or is it something new?

I think he was doing Vertical(nonparallel sculpting)a increase-layered cut.And instead of cutting the form blunt, he was notching the form for a softer line.I could be wrong but thats what it look like to me.

What happens is that when you are cutting an extreme angle (short bangs to long length, like Jonathan was doing), it is hard to get your body in a position to cut the same line on both sides of the head. So 'step' cutting (like you saw on the tv show) allows the sides to be layered equally on both sides and since the hair is being brushed back when it is styled you won't see the steps in the layering, it will also allow the layered pieces to separate more than if a straight smooth line was cut.

thats what I thought as I had that style for years and years, No my front is thinning and I can't wear it back the same as I did then. Plus my hair is so long now I can't get my self to cut it. I just did a trim last night and that hurt to do ! LOL